In recent years, thermal transfer systems have been developed to obtain prints from pictures that have been generated from a camera or scanning device. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to one of the cyan, magenta or yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen.
Dye receiving elements used in thermal dye transfer generally include a support (transparent or reflective) bearing on one side thereof a dye image-receiving layer, and optionally additional layers. The dye image-receiving layer conventionally comprises a polymeric material chosen from a wide assortment of compositions for its compatibility and receptivity for the dyes to be transferred from the dye donor element. Dye must migrate rapidly in the layer during the dye transfer step and become immobile and stable in the viewing environment. Care must be taken to provide a receiving layer which does not stick to the hot donor as the dye moves from the surface of the receiving layer and into the bulk of the receiver. An overcoat layer can be used to improve the performance of the receiver by specifically addressing these latter problems. An additional step, referred to as fusing, may be used to drive the dye deeper into the receiver.
In sum, the receiving layer must act as a medium for dye diffusion at elevated temperatures, yet the transferred image dye must not be allowed to migrate from the final print. Retransfer is potentially observed when another surface comes into contact with a final print. Such surfaces may include paper, plastics, binders, backside of (stacked) prints, and some album materials.
A variety of polymers are known to be useful in image-receiving layers. Such polymers include, polycarbonates, bisphenol-A polycarbonates, as set forth in U.S. Pat. No. 4,695,286 and U.S. Pat. No. 4,927,803, both incorporated herein by reference, polyesters formed from aromatic diesters (such as disclosed in U.S. Pat. No. 4,897,377, incorporated herein by reference), polyesters formed from alicyclic diesters are disclosed in U.S. Pat. No. 5,387,571 of Daly, incorporated herein by reference, phenyl group (e.g. bisphenol A) modified polyester resin synthesized by the use of a polyol having a phenyl group as the polyol compound as disclosed in U.S. Pat. No. 4,908,345 to Egashira et al., incorporated herein by reference, a polyester resin having a branched structure as disclosed in U.S. Pat. No. 5,112,799, incorporated herein by reference. Blends of polymers are also useful, for example, a miscible blend of an unmodified bisphenol-A polycarbonate having a number molecular weight of at least about 25,000 and a polyester as disclosed in U.S. Pat. No. 5,302,574 to Lawrence et al., incorporated herein by reference, and unmodified bisphenol-A polycarbonates of the type described in U.S. Pat. No. 4,695,286, incorporated herein by reference, may be blended with the modified polycarbonates of the type described in U.S. Pat. No. 4,927,803, incorporated herein by reference.
U.S. Pat. No. 6,897,183, incorporated herein by reference, relates to a process for making a multilayer film, useful in an image recording element, where the multilayer film comprises a support and an outer or surface layer wherein between the support and the outer layer is an “antistatic tie layer” comprising a thermoplastic antistatic polymer or composition having preselected antistatic properties, adhesive properties, and viscoelastic properties. In one embodiment of the invention, such a multilayer film is used in making a thermal-dye-transfer dye-receiver element comprising a support and an dye-receiving layer wherein between the support and the dye-receiving layer is a tie layer. However in U.S. Pat. No. 6,897,183, no mention of importance of tie layer adhesion to the dye receiver layer and to the support during printing and immediately after printing is made. Also, no mention is made of the importance of printing under hot and humid conditions, and lack of humidity sensitivity of the tie layer compositions. A preferred tie layer composition that takes into account the above factors is not disclosed in the reference. U.S. Patent Publication No. 2004/0167020, incorporated herein by reference, is also similar to U.S. Pat. No. 6,897,183 in that it does not make any references to adhesion of the dye receiver layer to the support during printing, immediately after printing, printing under hot and humid conditions, humidity sensitivity of tie layer compositions and preferred tie layer composition that takes into account these factors.
Known polymer laminates used on the faceside of thermal receivers have a top skin layer of polypropylene (PP) onto which is extruded a dye receiver layer (DRL) of polyester/polycarbonate blend. A conventional tie layer used between the laminate support and the dye receiving layer (DRL) is antistatic and is a blend of 70 wt % PELESTAT® 300 (polyethylene-polyether copolymer) and 30 wt % polypropylene (PP). The rheology of the two components is such that PELESTAT® 300 encapsulates the polypropylene (PP), so that the continuous phase in the tie layer is PELESTAT® 300. The PELESTAT® 300 acts as an antistatic material as well as an adhesive component to polymer laminate support skin layer and the dye receiving layer (DRL). This tie layer, however, is significantly humidity sensitive and has poor adhesion and does not survive borderless printing (edge to edge) when tested under hot and humid conditions like 36° C./86% RH.